ABS discs sometimes cost more depending on if the ABS sensor works off the hub or the disc. In my car, the ABS sensor is in a sealed hub so a front brake job is trivial. In my friend's ford ranger, the ABS is part of the disc AND the hub and bearings are integrated into the disc, so changing or turning his front rotors involves a complete bearing repack or replacement job, which is quite a bit more involved than a mere rotor/pad job. Plus the ABS system on my friend's truck includes a stamped steel ring attached to the rotor, and that ring is not present on non-ABS rotors so if you have ABS but get the wrong rotors, you may lose ABS if your car is like this particular FORD design.
You should check a service manual or chiltons guide for your car to see what is involved and to make sure you get the right parts.